Help with modeling a turret's arm from Portal 2
This task is quite simple.


Add the torus.
Go to edit mode and cut the half of it (actually more than a half) in "face mode".
Flatten this figure a bit.
Use a preset viewpoint (any dot of navigation "cube" that lets you to see the figure at a whole).
Enable "Snap - Increment", choose tick strict snap to grid, and snap the figure to grid. Add three separate dots (left/right mouse button + Click). Snap them to grid too!







Select all (A button) and use Bisect. Connect dots to slice the figure.
Select  everything that you don't need and delete. Disable snap.







"Extrude along normals" this figure.







Voila! Then you can add other inner parts that are simpler.